1. Field of the Invention
The present invention relates generally to a de-inking module, more specifically, to an open flotation conventional de-inking module adopted in the recycled paper processing plants, in which, ink separation and removal constitutes a major task. The specific concerns of this invention are the concept and the equipment for the separation and removal of the ink, stickies and ash from the pulp slurry contaminated with ink, clay and stickies.
Waste paper, usually called by the public, is actually not a waste and a very valuable source of fiber for recycled paper mills. Recovery of fiber has been increasing due to the solid waste problem and the demand by industry as well. There are several kinds of recovered paper, such as old corrugated container, old news print, white grades with several sub categories. The old corrugated container is usually recycled with out any ink removal to produce brown grade paper and boards.
A majority of the old newsprint and other white grade paper are recycled into various valuable paper categories using the de-inking process. There are two types of de-inking called: washing and flotation. Flotation usually has a washing step in the subsequent steps and can be called a combination process. The washing de-inking without any ink purging using some kind of white water clarification is not true de-inking as the ink recycles in the system. It is less common to have washing as the sole de-inking process at present. The washing process does not help in handling large ink and other dirt particles whereas the flotation process separates and removes a wide range of particles including small particles.
Several types of chemistries are used in the de-inking process like hardness dependent calcium soap froth, hardness independent surfactant, enzymatic and so forth. All these chemistries help release the ink from the fiber and attach the ink particles to the air bubbles in a selective adsorption process. The process needs equipment to mechanically separate and remove the ink off the pulp suspension. This is commonly called a flotation cell in the de-inking mills.
A de-inking mill usually has re-pulping equipment called a pulper at the beginning of the process to repulp the recovered paper brought into the mill for recycling. The re-pulping is done with water and chemicals to aid the pulping and sometimes bleaching at the same time. De-inking agent is usually added in the pulper and gets well dispersed with the pulp. The ink release from the fiber is aided by the de-inking agent with the wetting of the fiber surface as well as swelling. The same surfactant helps in the froth flotation in the primary de-inking system for the formation of the foam and selective adsorption of the ink particles onto the air bubbles.
For the effective separation of the ink from the pulp suspension, the air bubbles should be formed mechanically inside the pulp suspension which raise to the surface on which the ink particles adsorb to float to the surface.
A flotation cell is very important in bringing air and dispersing the air to increase the collision frequency with the ink particles along with other unwanted hydrophobic materials. The higher the bubble-ink collision frequency the better the chances of ink attachment to the foam. Attaching as much ink as possible under given operating conditions flotation cells remove the foam using several techniques like overflow, scraping using paddles, pressure under enclosed vessel and so forth. Thus de-inking is accomplished in various ways within froth flotation technology.
The present invention is an open flotation de-inking module for recycled paper comprised of a flotation cell having an injector module and air control module used in conjunction to infuse micro air bubbles into pulp slurry to optimize the process of separating ink, clay, stickies and other floatable contaminants from the recycled pulp slurry.
Accordingly, the slurry is negatively pressurized as it accelerates through the injector drawing air from the air control module saturating the slurry with air bubbles before injection into the flotation cell whereupon the contaminants will adhere to the bubbles as they move to the surface forming a foam that is passively skimmed into reject compartments with the decontaminated pulp channeled from the floatation cell for further processing.
The flotation cell forms means for the air infused slurry to effervesce forming a foam having the contaminants therein, which are passively skimmed into an effluent line. The flotation cell is a cylindrical receptacle having a centrally disposed cylindrical reject line with a flared opening. Tangently extending from the flared reject line opening to the receptacle exterior wall is a planar skimmer plate diverting the foam into the reject line. The air infused slurry is tangently injected into the flotation cell creating a rotational current with a decontaminated slurry accept line also tangently extending from the flotation cell.
The present invention provides for variations of the placement of the feed and accept conduits and various shapes for the passive skimmer plate.
2. Description of the Prior Art
There are other de-inking apparatus. Typical of these is U.S. Pat. No. 2,793,185 issued to Albrektsson, et al on May 21, 1957.
Another patent was issued to Singer on Jul. 10, 1962 as U.S. Pat. No. 3,043,433. Yet another U.S. Pat. No. 4,157,952 was issued to Krofta on Jun. 12, 1979. Another patent was issued to Ortnet, et al. as U.S. Pat. No. 4,328,095 on May 4, 1982 and still yet another was issued on Jan. 27, 1987 to Zipperian as U.S. Pat. No. 4,639,313.
Another patent was issued to Szatkowski; et al. on Apr. 12, 1988 as U.S. Pat. No. 4,737,272. Yet another U.S. Pat. No. 5,273,624 was issued to Chamberlain, et al. on Dec. 28, 1993. Another was issued to Carlton, et al. on Jun. 25, 1996 as U.S. Pat. No. 5,529,190.
Another patent was issued to Bodnaras on Jun. 9, 1998 as U.S. Pat. No. 5,762,781. Yet another U.S. Pat. No. 6,082,549 was issued to Gommel, et al. on Jul. 4, 2000. Another was issued to Scherzinger, et al. on Jul. 1, 2003 as U.S. Pat. No. 6,585,854. Still another was issued to Xu, et al on Nov. 1, 2005 as U.S. Pat. No. 6,959,815 and another was issued as U.K. Patent No. GB2144729 to Lecoffre, et al. on Mar. 13, 1985.